This invention relates generally to fire retarding polymers, and more particularly to a fire retarding polypropylene.
In the manufacture of semiconductors, clean rooms must be used. The semiconductor chip processing equipment and other equipment in the clean rooms, such as wet benches, wafer storage cabinets, and the like, must meet certain flammability tests. Factory Mutual Research Corporation (FMRC) has proposed a flammability standard for clean room equipment, entitled xe2x80x9cFMRC Clean Room Materials Flammability Test Protocolxe2x80x9d (Rev. 2.0, February 1997) (the xe2x80x9cFM 4910 Standardxe2x80x9d). Recommendations pertaining to the instant invention are found in Loss Prevention Data, Semiconductor Fabrication Facilities, (Factory Mutual Engineering Corp., 1997), Section 2.4 Processing Tools and Product Storage. Section 2.4.1 of this publication requires that new wet benches and other processing tools be constructed of noncombustible materials. xe2x80x9cExisting wet benches of combustible construction handling corrosive products should be replaced by wet benches in compliance with Section 2.4.1xe2x80x9d (Section 2.4.3). xe2x80x9cNoncombustible materials, or materials which are FMRC specification tested to meet the FMRC Clean Room Materials Flammability Test Protocol criteria should be used for mini-environment enclosuresxe2x80x9d. (Section 2.4.6).
When there is a fire in a clean room, damage can occur from the fire, the smoke, and/or the corrosive combustion by-products. Even when the damage from the fire is minimal, the smoke and corrosive combustion by-products can ruin the products and the processing equipment and other equipment in the clean room. Thus, even a small fire can cause enormous monetary loss.
Materials which pass the FM 4910 Standard can be made into semiconductor chip processing equipment and clean room equipment without the necessity of providing additional fire detection and suppression equipment, also termed fixed fire protection. This is desirable because false alarms from fire equipment can result in lost wafer production, and consequently, monetary loss. Therefore, materials which pass the FM 4910 Standard are preferred for use in semiconductor chip processing equipment and clean room equipment.
Various materials have been used in the manufacture of semiconductor chip processing equipment and clean room equipment. Thermoplastic materials such as polyvinylidene fluoride (PVDF), perfluoroalkoxy (PFA), polyether ether ketone (PEEK), and polytetrafluoroethylene (PTFE) have been used. While these thermoplastics pass the FM 4910 Standard and therefore can be used without additional fire detection and suppression equipment, they are relatively expensive polymers.
Polyolefin materials, including polypropylene, have also been used for semiconductor chip processing equipment and clean room equipment. Polypropylene, FR-Polypropylene and PVC in semiconductor applications are not used for wetted parts or primary process chemical containment. These materials are used in corrosive wet tool construction as a structural material. They typically compose the plastic box that encloses the process vessels, chemical delivery systems, robots, etc. They also have the function of the process vapor containment and in some applications they are used in plenum drainage and also serve to provide short term containment of process chemicals from process vessel failure. Contact with process fluids is either dilute, intermittent contact, i.e., plenum drainage, or it occurs as the result of splashing while filling process vessels or dripping while transferring wafer boats. The use of polyolefins is advantageous because they are inexpensive polymers. However, no fire retardant polyolefins have been able to pass the FM 4910 Standard. Consequently, fire detection and suppression equipment are required for semiconductor chip processing equipment and clean room equipment made of polyolefins.
Therefore, there is a need for an inexpensive, flame retarding polyolefin composition which will pass the FM 4910 Standard. The composition should be easily processable and capable of being formed into semiconductor chip processing equipment and clean room equipment. The composition should have the necessary physical properties so that it can be used to make the equipment.
The present invention provides a flame retarding polypropylene composition (FRPP) that meets the fire resistance requirements for semiconductor clean room materials developed by FMRC in the FM 4910 standard. The composition resists fire propagation and limits smoke and corrosive combustion by products beyond the ability of previous fire retarding polyolefins. This eliminates the need for fire detection and suppression devices (fixed fire protection).
Polypropylene resin pellets and a surface treated magnesium hydroxide (Mg(OH)2) are thermoplastically mixed into pellets. The plastic pellets can then be extruded, compression molded or injection molded into the desired form. High loadings of magnesium hydroxide, greater than 50%, render polypropylene resistant to propagation of fire, smoke and corrosive combustion by-products. Although high loadings of Mg(OH)2 ordinarily render polypropylene too brittle to use as construction material, this is avoided in the instant composition by using a surface treated Mg(OH)2, Kisuma 5A, 5B, or 5J (Kyowa Chemical Industry Co. Ltd., Tokyo distributed in U.S. by Mitsui) as disclosed in Miyata et al., U.S. Pat. No. 4,098,762 and Miyata et al., U.S. Pat. No. 4,145,404, and a specialized reactor copolymer polypropylene resin in which ethylene-propylene rubber has been grafted onto the polypropylene chains to act as an interchain shock absorber. This results in a highly ductile material.
The composition of the instant invention meets all the requirements for Factory Mutual Listing for the FM 4910 Standard. The material exhibits extreme resistance to ignition and fire propagation and yields low smoke and corrosive combustion by-products. It is both impact resistant and rigid and thus ideal for structural materials. It has excellent thermoplastic weld strength and is machinable. It has both high impact resistance and high flex modulus.